Pertaining to the game of baseball, ERA (Earned Run Average) is a statistical measure of the effectiveness of a pitcher. It is computed by the following formula:

ERA = (earned runs allowed)*(9)/(innings pitched)

Obviously, the lower the ERA, the more effective the pitcher, with an ERA of around 1.50 or below being considered excellent.

If Tim Hudson, starting pitcher for the Atlanta Braves, pitches 38 innings spread out over the first 6 games of the season, and allows 4 earned runs during those games, his ERA would be (4*9)/38 or 0.95. Thus he would be seen to be an extremely effective pitcher.